Semiconductor memory devices may be classified into volatile memory devices and nonvolatile memory devices. Volatile memory devices lose their stored data when their power supplies are interrupted. Examples of volatile memory devices are dynamic random access memory (DRAM) devices and static random access memory (SRAM) devices. Nonvolatile memory devices can maintain their stored data even when their power supplies are interrupted. Examples of nonvolatile memory devices are erasable programmable read only memory (EPROM) devices, electrically erasable programmable read only memory (EEPROM) devices and flash memory devices.
As the electronics industry and the semiconductor industry advance, the desire for even greater integration of nonvolatile memory devices is increasing. For example, as more capable portable electronic devices, such as laptop computers, cell phones, digital cameras and MP3 players, are developed, the demand for nonvolatile memory devices capable of storing more data are increasing. Accordingly, the desire for more highly integrated nonvolatile memory devices is increasing.
A common way of achieving greater integration of nonvolatile memory devices is to decrease a minimum line width of fine patterns in the device. Generally, more memory cells can be integrated in a limited area by decreasing the minimum line width of fine patterns. However, the ability to decrease minimum line width is approaching a limit using conventional technologies. For example, a minimum line width that conventional photolithography processes can define appears to be approaching a limit such that, if line width is further decreased, the accuracy of fine patterns may deteriorate, resulting in degradation of reliability.